COGENERATION

PRINCIPLES OF COGENERATION

Cogeneration is a way of generating both thermal energy and electricity. In convectional thermal power stations outlet steam needs to be cooled before pumping it to the boiler again. The heat wasted during the cooling is the highest energy loss in the whole generation process and it is the main reason why thermal power systems have such a low efficiency. Cogeneration allows for using the waste heat and thus enhancing the overall system efficiency.

The differences between cogeneration system and separate generation of heat and power are shown on Figure 5, where principles of generation of thermal energy and electricity are presented. Looking at separate generation, on the premise that electricity is generated with efficiency of 35% there are 60 units of primary energy needed to create 21 units of electricity. To generate 33 units of heat there are 37 units of primary energy required, thus the total amount of primary energy used in that system is 97 and the overall efficiency totals 55%. Cogeneration perceptibly improves overall efficiency and provides the same amount of energy when only 60 units of primary energy is used.

  • FIGURE. 5.: THEORETICAL GENERATION OF ENERGY IN SEPARATED GENERATION AND COGENERATION BASED ON [5]

    • Production of heat is vital during cold seasons when heat demand is high but there are months in a year when it is rather inefficient. Graph. 1 shows a theoretical graph of heat and coolness demand within twelve months period. As it can be seen, from April to September that the cooling demand is higher than heat demand and it would be very positive to generate cool energy instead of hot one during those seasons. The technology which allows for generation electricity and the use of the waste heat for heating and cooling is trigeneration.

  • GRAPH. 1: THEORETICAL DEMAND OF HEAT AND COOLNESS

    • Trigeneration uses absorption refrigerators which basically convert a heat source into coolness. This improves the overall efficiency of the entire generation process and makes it more useful. However, it also has some disadvantages. One of the biggest weakness of trigeneration is that this system is relatively immature and following on that not researched enough.

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